The group of four Vietnamese nationals and two Vietnamese individuals with US nationality were found dead at Grand Hyatt Erawan hotel in Ratchaprasong shopping district in Pathum Wan district by hotel maids.
By the time the police entered the hotel room, there were a variety of food dishes and drinks inside the room.
The police examined the scene and initially said there were no signs that the victims had been robbed or assaulted before they died.
Pol Maj Gen Theeradet Thumsuthee, investigative commander of the Metropolitan Police Bureau, said authorities were exploring the possibility that the victims have been poisoned as there were coffee and tea in the room.
However, it is still unclear whether they took their own lives or were poisoned.
Thai Prime Minister Srettha Thavisin also rushed to the scene in the evening and confirmed the news.
“We need to conduct an autopsy to see if they had ingested anything,” the prime minister said after working with the police.
The police hold a press briefing in the evening informing media outlets about the case
Ratchaprasong is a shopping and entertainment area located next to the Siam Paragon shopping mall in the heart of Bangkok. Last year, a teenager was arrested after shooting dead two foreigners at the Siam Paragon shopping mall.